This project's objectives are to characterize the formation and repair of DNA damage after treatment of mammalian cells with anti-tumor agents. In addition to the use of standard methods, such as alkaline sedimentation, a major part of this work involves the development and application of a new set of techniques known as DNA alkaline elution analysis. These techniques now provide means to estimate the following types of DNA damage at pharmacologic dosage levels: single-strand breaks, alkali-labile sites, DNA-protein links, and DNA interstrand crosslinks. The drugs studied during the past year include nitrogen mustard (HN2), melphalan, cis-Pt(II), and nitrosoureas--including BCNU, CCNU, MeCCNU, chlorozotocin, and methylnitrosourea. The kinetics of formation and repair of various types of DNA damage have been examined in mouse L1210 cells, and in human embryo cells--both normal and viral-transformed, Burkitt lymphoma cells, and in human colon carcinoma lines--both in nude mice and in cell culture. These studies are aimed at elucidating the way in which DNA damage may lead to cell death, particularly differential cytotoxicity, and providing means by which predictive sensitivity tests might be developed for clinical applications. BIBLIOGRAPHIC REFERENCES: Kohn, K.W.: Interstrand Cross-linking of DNA by 1,3-Bis(2-chloroethyl)-1-nitrosourea and Other 1-(2-haloethyl)-1-nitrosoureas. Cancer Res. 37, 1450-1454, 1977. Ewig, R.A.G., and Kohn, K.W.: DNA Damage and Repair in Mouse Leukemia L1210 Cells Treated with Nitrogen Mustard (HN2), 1, 3-Bis(2-chloroethyl)-1-nitrosourea and Other Nitrosoureas, Cancer Res. 37, 2114-2122, 1977.